My invention relates to thyristors in general and, in particular, to a bidirectional triode thyristor known as the Triac (trademark owned by the General Electric Company). More particularly, my invention pertains to such a thyristor of improved trigger characteristics.
The Triac has found widespread use as an alternating-current (a.c.) power switch in electronic circuits such as those for motor control. U.S. Pat. No. 3,739,242 to Foster represents a known Triac configuration designed for a high triggering sensitivity. For the achievement of a high triggering sensitivity, Foster teaches to provide two peninsular portions of n-type regions defining an elongate portion of a p-type region therebetween.
I object to this and comparable prior art Triac constructions because the width of the elongate p-type portion cannot possibly be reduced indefinitely by reason of the requirement for electrical separation between the two n-type regions. Thus, as there is a limit to the reduction of the width of the elongate p-type portion, so there has been a limit to a degree of triggering sensitivity attainable.